This invention relates generally to pressurized fluid-containing devices and, more particularly, to an apparatus and associated methods of operation such as for use in the inflation of an inflatable device. More specifically, the invention relates to an apparatus and associated methods of operation such as for use in the inflation of inflatable devices such as inflatable vehicle occupant restraint airbag cushions used in inflatable restraint systems.
It is well known to protect a vehicle occupant using a cushion or bag, e.g., an "airbag cushion," that is inflated or expanded with gas such as when the vehicle encounters sudden deceleration, such as in the event of a collision. In such systems, the airbag cushion is normally housed in an uninflated and folded condition to minimize space requirements. Upon actuation of the system, the cushion begins to be inflated, in a matter of no more than a few milliseconds, with gas produced or supplied by a device commonly referred to as an "inflator."
"Rise rate", i.e., the rate at which the gas output from an inflator increases pressure, as measured when such gas output is directed into a closed volume, is a common performance parameter used in the design, selection and evaluation of inflator devices for particular vehicular airbag restraint system installations. It is commonly desired that an inflatable restraint airbag cushion initially inflate in a relatively gradual manner, soon followed by the passage of inflation gas into the airbag cushion at a relatively greater or increased pressure rate. An inflator resulting in such inflation characteristics is commonly referred to in the field as producing inflation gas in accordance with an "S" curve.
Many types of inflator devices have been disclosed in the art for the inflating of one or more inflatable restraint system airbag cushions. One category of such inflator devices is often referred to as "compressed gas inflators" and refers to various inflators which contain a selected quantity of compressed gas. For example, one particular type of compressed gas inflator, commonly referred to as a "stored gas inflator," simply contains a quantity of a stored compressed gas which is selectively released to inflate an associated airbag cushion.
A second type of compressed gas inflator, commonly referred to as a "hybrid inflator," typically supplies or provides inflation gas as a result of a combination of stored compressed gas with the combustion products resulting from the combustion of a gas generating material, e.g., a pyrotechnic.
Commonly assigned Smith et al., U.S. Pat. No. 5,470,104, issued Nov. 28, 1995; Rink, U.S. Pat. No. 5,494,312, issued Feb. 27, 1996; and Rink et al., U.S. Pat. No. 5,531,473, issued Jul. 2, 1996 disclose and relate to a new type of inflator device, sometimes called a "fluid fueled inflator." Such inflator devices typically utilize a fuel material in the form of a fluid, e.g., in the form of a gas, liquid, finely divided solid, or one or more combinations thereof, in the formation of an inflation gas for an airbag cushion. In one form of fluid fueled inflator, such a fluid fuel material is burned to produce gas which contacts a quantity of stored pressurized gas to produce inflation gas for use in inflating a respective inflatable device.
A more recently developed inflator device is at least in part the subject of commonly assigned Rink, U.S. Pat. No. 5,669,629, issued Sep. 23, 1997; Rink et al., U.S. Pat. No. 5,884,938, issued Mar. 23, 1999; and Rink et al., U.S. Pat. No. 5,941,562, issued Aug. 24, 1999, the disclosures of which patents are hereby and expressly incorporated herein in their entirety. In one form of such newly developed inflator device, inflation gas is produced or formed, at least in part, via the decomposition or dissociation of a selected gas source material, such as in the form of a compressed gas and such as via the input of heat from an associated heat source supply or device.
Specific categories or types of compressed gas inflator devices include those commonly referred to as "blow down" and those referred to as "direct opening" inflation systems. In a blow down inflation system, a pyrotechnic or other selected material is commonly burned to create a build-up of pressure within a compressed gas storage chamber such as to result in the rupture or release of inflation gas therefrom when the internal pressure reaches a predetermined level or range. In contrast, in a direct opening type inflation system, compressed gas is commonly released as a result of the movement of a mechanical opening device such as an associated projectile or piston member.
While blow down inflation systems can desirably be of relatively lower cost and complexity, such systems can result in the delivery of inflation gas to an associated airbag cushion at a higher temperature, pressure and/or mass flow rate than may otherwise be desired. In contrast, direct opening inflation systems typically permit a portion of the associated stored compressed gas to be released prior to any substantial heating thereof such as typically results upon the thermal contact thereof with the combustion products resulting from combustion of the associated gas generating material. With such initial release of unheated gas, the inflation gas initially delivered during the first few moments upon actuation is typically at a relatively low pressure, thus desirably providing a form of the above-described S curve inflation performance behavior. In particular, such operation can advantageously provide what is commonly termed as a "soft deployment" of the associated airbag cushion. As known in the art, such soft deployments can be desired in various circumstances such as in the event the corresponding vehicle occupant is out-of-position for what is normally considered optimal protection via the restraint system.
Unfortunately, the use of or reliance on mechanical opening devices such as projectiles or piston members in such direct opening inflation systems may result in inflation systems which may be either or both more costly or complicated than desired.
Thus, there is a need and a demand for an inflation system and particularly an inflator apparatus and method of operation which can desirably provide for a soft deployment of an associated airbag cushion without necessitating the use of or reliance on mechanical opening devices such as projectiles or piston members, the use or operation of which may be either or both more costly or complicated than desired.
Further, in view of possibly varying operating conditions and, in turn, possibly varying desired performance characteristics, there is a need and a desire to provide what has been termed an "adaptive" inflatable restraint system. With an adaptive inflatable restraint system, one or more parameters such as the quantity, supply, and rate of supply of inflation gas, for example, can be selectively and appropriately varied dependent on one or more selected operating conditions such as ambient temperature, occupant presence, seat belt usage, seat position of occupant and rate of deceleration of the motor vehicle, for example.
While such adaptive systems are desirable, they typically require the inclusion of additional components either in the system or as a part of the associated inflator device itself. Such inclusion of one or more additional components may undesirably increase the size, cost and/or weight of the inflator device or associated system. For example, various proposed or currently available dual stage inflator devices, particularly pyrotechnic-based forms thereof, appear based on the principal of packaging together two separate inflators. As a result, such inflator combinations commonly include two distinct pressure vessels, two sets of filter or inflation gas treatment components, one for the output of each of the pressure vessels, and two distinct diffusers, again one for the output of each of the pressure vessels. Thus, it has been difficult to provide an adaptive inflator which will satisfactorily meet the size, cost and weight limitations associated with modern vehicle design.
Stored or compressed gas-based adaptive inflation systems may overcome or at least minimize certain of such disadvantages. For example, such corresponding inflator devices may contain or utilize a single or "common" gas storage chamber for the provision of two or, possibly, more levels of performance or inflation pressures such as by selectively heating the stored gas to selected higher levels of pressure. Nevertheless, there is a need and demand for even more flexible inflation systems such as may capably provide an even wider array of selectable performance options.
For example, a common problem with typical or conventional stored gas adaptive output inflator designs is a lack of a desired range of outputs between the standard output and adaptive output of such inflator devices (such as measured in terms of pressure in a closed tank). Typically, the second or "adaptive" level pressure is only 10% to 30% (perhaps) of the total output of the inflator. In practice, those skilled in the art commonly refer to the performance "split" of an adaptive inflator. For example, if an inflator produces an output of 25 psi in the single stage "standard" mode, and 50 psi with the firing of both standard and adaptive stages, such an inflator is said to display a 50--50 "split". In other words, the performance split is the fraction that each stage "standard" and "adaptive" contributes to the maximum performance. Thus, typical stored gas adaptive output inflators typically produce a performance split of up to about 70-30.
In addition, stored gas hybrid inflators most commonly store or contain inert gas. Thus, the adaptive output or additional performance obtainable therefrom largely results from volume expansion of the stored gas such as due to heat provided or supplied from an additional pyrotechnic charge. In particular, if the pyrotechnic charge simply produces heat (no gas) there is no increase in molar (volumetric) output of the inflator under such adaptive output conditions. If the pyrotechnic charge does produce some gas as well as heat, the additional gas molar output is usually quite small. Thus, the performance splits readily obtainable with such hybrid inflators are typically directly a function of the amount of pyrotechnic which can be packed into the adaptive stage before the internal pressures generated become too severe for practical construction. Further, as pyrotechnic materials can be relatively expensive and difficult to manufacture, the use and reliance of increased pyrotechnic loads may render such approaches economically unattractive.
Thus, there is a need and a demand for an adaptive inflation system which more readily permits or otherwise allows a desirably greater range in performance capabilities, such as may more readily provide desired or required design and application flexibility.